High-pressure rubber hose is used in many instances in industry but particularly in the mining, construction, energy, marine and petrochemical industries. Flexible rubber hose is used to transfer fluids under various pressures and temperature between two points, one or both of which, may move relative to each other or to another fixed point in space. Piping at the two points is generally metal (or some other form of fixed conduit) and the flexible hose must attach to the piping at both ends. This requires a coupling on each end of the hose.
In the drilling industry, a flexible rubber hose runs between the pump piping system on the rig and the kelly that is coupled to the rotating drill string. The pump system forces drilling fluid down the center of the drill pipe, and back through the wellbore, in order to flush cuttings from the wellbore (plus providing wellbore stability, etc.). In this instance, the flexible hose is subjected to high pressures. The high pressure is required to both transfer drilling fluid into the wellbore and overcome static return head pressures—the deeper the wellbore, the higher the pressure.
The rotary drilling hose is subject to further stress in that it hangs down within the derrick supported at either end by the metal coupling on the hose and the fact that the kelly is moved up and down literally thousands of times during the drilling operation. This means that the hose is subject to stress at the metal coupling (in addition to being subject to stress throughout its length). Thus, a highly reliable bond between the hose and the coupling is required for protection of personnel and equipment. If the hose breaks loose from the coupling, it could easily fall and cause severe damage on the drill floor of the rig. In a similar manner, if the hose breaks, circulation may be lost resulting in a well blowout situation.
In order to obtain a high-pressure flexible rubber hose (the term rubber is used generally and does not specifically mean natural occurring rubber gum), a hose manufacturer incorporates a reinforcing material. Thus, the hose will consist of an inside sealing membrane—the fluid tight element, an inner rubber element, a reinforcing element, an outer rubber element, and finally some sort of abrasive resistant covering. The reinforcing element can be polyester or similar organic material, carbon fiber or similar high technology material or metal (steel) generally in the form of wire or cable. The reinforcement generally is used in multiple layers called “plys” And usually made of steel.
There are four types of reinforcing employed by the hose manufacturer that is set down in even layers—i.e., 2 layers, 4 layers, 6 layers, etc., and grading systems are used to specify burst pressures for hose. For example, in the rotary drilling industry, grade C hose has a minimum burst pressure of 10,000 psi, grade D hose has a minimum burst pressure of 12,500 psi and grade E hose has a minimum (guaranteed) burst pressure of 18,750 psi. Grade C and D hose are 2 ply hose, although there is some 4 ply D hose. Most grade E hose is 4 ply. Swage end connectors are currently available for two ply hose and therefore the burst pressure range for C and D hoses is covered by the current art.
Generally a hose manufacturer manufactures flexible hoses to specific order by the purchaser who specifies length, diameter, pressure, service ratings and required end connections. These flexible hoses are generally referred to as a “hose assembly with end connectors” or “a built-up hose assembly.” This term is used throughout the industry.
In a built up hose assembly with end connections, the manufacturer, during the course of manufacturing terminates the rubber hose into a metal fitting (the end connector) as specified by the purchaser. Thus, the manufacturer would make the inner rubber membrane (1st Carcass) and its associated inner seal layer (tube or inner tube) and terminate this assembly in the end connector. The manufacturer would then add the wire reinforcement, as needed, terminating each reinforcing wire (or cable) in the end connector. Two techniques are typically employed by hose manufacturers for terminating the wire reinforcing in or on the end connector itself but are beyond the scope of this discussion. Finally the outer rubber layer (2nd Carcass) and outer cover (cover) would be formed about the reinforcing wire or cable and the overall product vulcanized to achieve a cohesive product.
It takes time to manufacture a hose assembly with end connections by this method and often such a hose is needed almost immediately by industry. In order to service this demand a separate industry termed the local market distributor has evolved. The local market distributor keeps bulk reinforced hose—hose without connectors—in inventory. The purchaser would specify the hose requirements—diameter, length, pressure rating and end connectors—to the local market distributor. The local market distributor then takes bulk reinforced rubber hose from inventory, cuts the hose to required length, and places a coupling on each end of the hose. Bulk hose is available in varying lengths from a hose manufacturer, and the actual bulk length (between 90 and 110 feet) will depend on the mandrel used by the manufacturer.
The resulting hose is called a SWAGED or CRIMPED HOSE, depending on the method used to “place” the end connector onto the hose, where the term “place” is being used to include both swaging and/or crimping operations. It should be noted that swaging and crimping accomplish similar end results.
The current state of the art in swaged (or crimped) connectors has evolved to using an outer ferrule with lands (internal ridges) that are compressed around the end of a reinforced hose about a stem that is inserted into the end of the hose. The stem may or may not have barbs that are meant to improve the “grip” between the hose and the end connector. Often, the outer layer of the reinforced hose is “skived” which means that the outer carcass (the outer layer of rubber and abrasive resistant covering) is removed thereby exposing the reinforcement (although some local distributors do not skive).
The reinforced hose is actually held in the end connector by the ridges of the ferrule gripping the reinforcement via compression of the hose against the stem. The compression operation (swaging or crimping) of the ferrule against the reinforcement and against the inner stem creates severe stress and strain within the rubber of the hose and in particular the reinforcement.
It is known that multiple ply-reinforced hose may contain manufacturing defects (actually all reinforced hose may contain defects). During manufacture a ply may be out of position. That is, rather than lie next to each other a void (filled of course with rubber) may exist between the plys; the plys may be off-center; or, one or more cables may stand out (i.e., be slightly above the other cables). These defects can cause failure, if the defect is within or near the confines of the swaged or crimped connection.
The reason for the failure is relatively simple and relates back to stress imposed on the plys by the end connector. If a cable or ply is out of place, that element will be compressed more than the other elements. This additional compression puts more stress on the out-of-place reinforcement that can result in failure.
Development of high pressure swaged end connectors for rubber hose has extended over a period of years and the art runs the gauntlet from low temperature and/or low pressure to high temperature and/or high pressure applications. The hose diameters range from fractional centimeters [fractional inches] to fractional meters [tens of inches] and the manufacturers/providers of connectors realize that the pump-off force on the fitting is proportional to the inside diameter of the hose and the applied pressure.
As explained in U.S. Pat. No. 7,338,090 to Baldwin et at., which is incorporated in its entirety in this disclosure by reference, most of the standard prior art uses a serrated stem that has backward facing teeth that grips the inner liner of the hose to retain the stem in the hose. Further the art also uses a series of lands (ridges) within the ferrule that bite into the outer layer of the hose and the reinforcement and supposedly causes the teeth (or barbs) of the stem to bite further into the inner lining.
Baldwin et al. explain that the standard art causes severe failure of the reinforcing cable (or wire) because the sharp edges of the connector damage the reinforcement. In order to overcome this basic failure Baldwin et al. proposed an invention that consisted of a “waved” ferrule and stem that joins an end connector to flexible reinforced rubber hose thereby forming a “double sine-wave lock” between the ferrule and the stem, but mainly the lock forms within the ferrule (see U.S. Pat. No. 7,338,090). The ferrule and stem are welded together at the coupling end leaving an opening, which accepts the reinforced rubber (elastomer) hose in almost the same manner as a normal “ridged” ferrule and “barbed” stem fitting. Rather than having straight sides, the lands of the ferrule and the high points of the stem form a sinusoidal shape-wave. The wave pattern has the appearance of ripples on a pond caused by throwing a stone into the water.
The ‘double sine-wave lock’ invention locks all the plys of hose reinforcement inside the end connector, between the stem and ferrule, in a sine wave compressed against the ferrule and the stem to give the fitting an overall strength that is in excess of the strength of the free standing hose (without end connectors) whether or not the hose is under pressure. Grade E hose has a minimum burst pressure of 18,750 psi; thus the instant device, when used with grade E hose will have an overall strength greater than 18,750 psi. (At these pressures the pump-off forces involved reach or exceed 240,000 poundsforce depending on the cross sectional areas.) The invention carefully considers the material forming the ferrule and stem and the relative movement of those materials while attaching the end connector to the hose along with the unpredictable qualities of rubber and flexible hose construction to minimize induced stress in the hose reinforcement. All of these factors, including the sinusoidal shape of the ferrule and stem and the preferred two-step method of attachment (internal expansion of the stem followed by external swaging of the ferrule), operate together to form the original Baldwin et al. invention.
In overall summary, the original Baldwin et al. ‘double sine-wave lock’ invention utilizes a sinusoidal wave-like lock within a ferrule and stem to lock the reinforcement plys and the hose into the end connector by compressing the hose and reinforcement between the waved ferrule and waved stem. Stress and strain on the reinforcement and the tendency for the reinforcement to tear (or pull away) from the rubber hose is minimized by carefully reducing the relative axial displacement between the ferrule and stem that always occurs during the attachment operation. The relative axial displacement is minimized by using high tensile strength steels, minimum un-attached clearances between the hose and end connector, and careful design of the node, lands grooves and flutes to cause a sine like wave while minimizing the radial thickness of the stem and ferrule at the critical cross-sections and considering the resulting strength of the attached fitting.
The Baldwin ‘double sine-wave lock’ has proven to work with any cable or wire high pressure reinforced hose and has in fact replaced the ‘built-up’ hose with end connectors, because the hose that utilizes the Baldwin double sine-wave end connector will not fail between the hose and the end connector. Any failure of the hose under pressure will be in the hose itself. THE END CONNECTOR WILL NOT COME LOOSE FROM THE HOSE: this statement cannot be made regarding built-up hoses. Thus, the ‘double sine-wave lock’ Baldwin end connector has improved safety in the workplace. No longer will a hose come loose and flop all over the area damaging equipment and injuring personnel.
The “double-lock” end connector requires a two step connection process. The connector is placed on the hose and the stem is internally expanded. The resulting assembly is then placed in a swaging press and the ferrule is swaged onto to the hose/stem. In developing their invention, the inventors wondered if such a two step process was needed and if large (relatively) lands and grooves were required on the stem. It was known that the actual lock occurred between the ferrule and the reinforcement with some minimal lock (transfer of pump-off force) between the stem and the reinforcement. If a stem could be designed with small bumps and if a connection step could be eliminated an improved device would result. More importantly, the removal of the expansion step would reduce the amount of material movement within the hose during the swaging/expansion process. With the reduction of material movement within the hose itself, an improved seal and lock could result with a reduction in induced stress.
In the past several years hose manufacturers (particularly in Europe) have been producing a light weight high pressure reinforced rubber hose. This hose uses wire or cable reinforcement but uses a much thinner inner tube. The inner tube is the non-leaking flexible conduit through which a high pressure fluid passes. The expansion force is transferred to the reinforcement which prevents the inner tube from bursting. In order to reduce the overall hose weight, the manufacturer is using a thin tube and a thin outer cover. As these materials become thinner, the requirement that movement between the components of the hose, (i.e., the inner tube, reinforcement and outer cover) becomes more critical. Thus there remains the need for a sine-wave lock device that produces minimal stress during the connection process between the connector and the reinforced hose used in rotary hoses and other high pressure rubber hoses.
The API (American Petroleum Institute, which produces the definitive standards for the industry) introduced stricter standards for rotary hoses in October 2006. These stricter standards resulted in three temperature ranges and three “Flexible Specification Levels (standards)” for high pressure rotary hose. The temperature standards are as follows.                Temperature Range I: −20° C. to +82° C. [−4° F. to +180° F.]        Temperature Range II: −20° C. to +100° C. [−4° F. to +212° F.]        Temperature Range III: −20° C. to +121° C. [−4° F. to +250° F.]        
The Flexible Specification levels are as follows.                FSL 0: Cement hoses only—no pulsation        FSL 1: Rotary, vibrator and jumper hoses—normal service only—no high frequency pulsation.        FSL 2: Rotary, vibrator and jumper hoses—likely to incur high frequency vibrations exceeding 6.9 MPa [1000 psi] during operation.        
Unfortunately, these new API standards caused a series of failures in most (if not all) swaged end connectors particularly in Temperature Range III and FSL 2 during testing. In the case of temperature range III, the inner tube (the actual liquid containing element in a high pressure reinforced) hose melts resulting in disengagement of the connector from the hose, leakage within the end connector or both. Unfortunately, the same failures happen in built-up hose and for the same reason. Neither of these conditions is tolerable and thus there remains a need for high pressure end connector that will meet the new API standards.